The present invention relates to liquid crystal display devices and, more particularly to fluorescent liquid crystal display devices comprising a liquid mixture having liquid crystal display materials and fluorescent materials dissolved therein. Light scattering conditions are caused within the fluorescent liquid crystal display devices in response to external excitations such as an electric field, whereby visible the fluorescence emitted from the fluorescent materials is effectively emitted from the liquid crystal display device.
Generally known electro-optical effects of liquid crystals are a dynamic scattering effect, twisted nematic electric field effect, guest-host effect, cholesteric-nematic phase transition effect, etc. These electro-optical effects provide displays by the scattering or absorption of ambient light, as distinct from the effects of luminescent materials which per se produce luminescent displays such as lamp displays, luminescent diode displays, electroluminescence displays, plasma displays or the like. The displays utilizing the electro-optical effects are advantageous over those of the latter type in that they involve reduced energy consumption however, they have the drawback of lacking brilliance.
It has been proposed to add a fluorescent material to a liquid crystal material and vary the fluorescent intensity of the material by electric field (Larrabee, R. D., RCA Review, Vol. 34, P 329, 1973). However, this paper states that the author failed to find liquid crystal materials which do not absorb ultraviolet light at room temperature. This appears attributable to the fact that when causing a fluorescent material in a liquid crystal material to absorb a varying amount of light in accordance with the orientation of the liquid crystal to vary the fluorescence intensity with the light absorption, the exciting light is absorbed by the liquid crystal layer without effectively exciting the fluorescent material.
U.S. Pat. No. 3,844,637 discloses fluorescent liquid crystal compositions comprising 4'-methoxy-(or -ethoxy-)benzylidene-4-n-butylaniline as a liquid crystal material. However, the compositions per se absorb violet light or near ultraviolet light without permitting effective excitation of the fluorescent material.